This invention relates to an image reproduction device, an image reproduction method, and an information storage medium that enable the reproduction of digital dynamic image data from analog dynamic image data (a signal) that was generated as digital dynamic image data then was converted into an analog signal.
Ordinarily, digital dynamic image data that was generated as digital data by an image generation device such as a TV game machine is subjected to analog conversion to produce analog dynamic image data that can be displayed on a TV screen or CRT monitor or the like.
However, it is often convenient to work on image data, such as dynamic image data, as digital data when subjecting such image data to processing. Examples include superimposing captions on the image data or transmitting the image data over a network.
In such a case, it is necessary to subject that analog dynamic image data to analog-digital conversion such that it ends up as close to the original digital dynamic image data as possible, and reproduce it as digital dynamic image data.
During the reproduction of this digital dynamic image data that was fetched as analog dynamic image data, if the analog-digital conversion is done with no connection to the timing at which the original digital dynamic image data was generated, the phase and frequency of the sampling clock will differ from those of the sampling clock for the original digital dynamic image data and the thus-obtained digital dynamic image data could be vastly different from the original digital dynamic image data.
A method called over-sampling is used to ensure there is no such difference, but this doubles the amount of digital data that is handled, making it necessary to increase the operating frequency of the circuitry and thus making it necessary to use more precise and more expensive hardware.
There is another method of reproducing the digital dynamic image data by fetching it during the original digital dynamic image generation, before it is subjected to digital-analog conversion, but this necessitates special hardware and software, and is thus not practicable.
This invention was devised in the light of the above described technical problem and has as an objective thereof the provision of an image reproduction device, image reproduction method, and information storage medium that can take digital dynamic image data that has been subjected to analog conversion and reproduce digital dynamic image data therefrom that is substantially the same as the original digital dynamic image data.
(1) According to a first aspect of the present invention, there is provided an image reproduction device for taking analog dynamic image data (a signal) obtained by performing an analog conversion of digital dynamic image data that was generated on the basis of a predetermined dot clock, and reproducing the digital dynamic image data therefrom, the image reproduction device comprising:
synchronization signal input means for inputting a synchronization signal for the digital dynamic image data;
clock generation means for generating a sampling clock which has the same frequency as that of the dot clock and which is also at a phase that is adjusted on the basis of the synchronization signal; and
analog-digital conversion means for digitizing the analog dynamic image data, based on the sampling clock, to reproduce the digital dynamic image data.
According to a second aspect of the present invention, there is provided an image reproduction method for taking analog dynamic image data (a signal) obtained by performing an analog conversion of digital dynamic image data that was generated on the basis of a predetermined dot clock, and reproducing the digital dynamic image data therefrom, the image reproduction method comprising the steps of:
inputting a synchronization signal for the digital dynamic image data;
generating a sampling clock which has the same frequency as that of the dot clock and which is also at a phase that is adjusted on the basis of the synchronization signal; and
reproducing the digital dynamic image data by digitizing the analog dynamic image data, based on the thus generated sampling clock.
According to a third aspect of the present invention, there is provided computer-usable information embodied on an information storage medium for implementing (executing) the above described means or steps. As an example of the information, there is a computer-usable program for implementing (executing) the above described means or steps. This program could be embodied in a carrier wave.
If the type of image generation device that generates and outputs the analog dynamic image data is known, the dot clock frequency for the digital dynamic image data that forms the source of the analog dynamic image data is identified thereby. If, for example, the image generation device is a game machine, the frequency of the dot clock used by that game machine can be identified from the type of the game machine.
Thus the image reproduction device of this invention receives the analog dynamic image data and also the synchronization signal that was used during the generation of the digital dynamic image data that is the source of this analog dynamic image data.
A sampling clock is then generated, based on a frequency corresponding to the dot clock for the pre-analog-conversion digital dynamic image data, which has been previously identified, and the input synchronization signal, so that this sampling clock has the same frequency as the dot clock and also has a phase that is adjusted to be suitable for sampling.
The thus-generated sampling clock is then used for sampling the input analog dynamic image data and thus reproduce the digital dynamic image data.
In this manner, during the regeneration of the digital dynamic image data from the input analog dynamic image data (signal), the digital data for each dot that configures this reproduced digital dynamic image data has substantially the same value as the digital data for each dot that configures the original digital dynamic image data as it was before the analog conversion. As a result, the image reproduction device can obtain digital dynamic image data that is faithful to the source image, without using the over-sampling method.
Note that RGB luminance signals or the like can be included in this analog dynamic image data, for example.
The synchronization signal used in this case could be both of the vertical synchronization signal and the horizontal synchronization signal, but the horizontal synchronization signal alone could be used, by way of example.
(2) According to a fourth aspect of the present invention, there is provided an image reproduction device for taking analog dynamic image data obtained by performing an analog conversion of digital dynamic image data that was generated by an image generation device, based on a predetermined dot clock, and reproducing the digital dynamic image data therefrom, the image reproduction device comprising:
synchronization signal input means for inputting a synchronization signal for the digital dynamic image data;
storage means for storing frequency data corresponding to the dot clock;
selection means for selecting frequency data for generating a sampling clock, from the frequency data stored in the storage means;
clock generation means for generating a clock at the same frequency as that of the dot clock, based on the selected frequency data, then generating the sampling clock from the clock, with a phase that is adjusted on the basis of the synchronization signal; and
analog-digital conversion means for digitizing the analog dynamic image data, based on the thus generated sampling clock, to reproduce the digital dynamic image data.
According to a fifth aspect of the present invention, there is provided computer-usable information embodied on an information storage medium for implementing the above described means. As an example of the information, there is a computer-usable program for implementing the above described means. This program could be embodied in a carrier wave.
A sampling clock corresponding to a dot clock can be easily generated by previously storing frequency data corresponding to that dot clock, thus making it possible to improve the efficiency with which digital dynamic image data is reproduced.
In this aspect of the invention, a plurality of sets of frequency data corresponding to different devices is stored, to suit a plurality of image generation devices having different digital dynamic image data generation means. This makes it possible to easily generate a sampling clock corresponding to each type of device, even when digital dynamic image data is input from a plurality of image generation devices.
Note that the selection means could be configured in such a manner that the frequency data could be selected automatically or manually.
In addition, it is preferable that the frequency of the dot clock of each of these image generation devices is previously checked, and data is stored in a frequency data storage means of each device, based on the results of the check.
(3) The storage means may store phase data corresponding to the dot clock; the selection means may select phase data for generating a sampling clock, from the phase data stored in the storage means; and the clock generation means may generate a clock at the same frequency as that of the dot clock, based on the frequency data and the phase data, then generate the sampling clock from the clock, with a phase that is adjusted on the basis of the synchronization signal.
This makes it possible to generate any desired sampling clock to correspond to the dot clock, then adjust the phase of the sampling clock on the basis of the synchronization signal, by using a configuration whereby phase data is previously stored in addition to the frequency data.
The above described configuration also makes it possible to reduce special processing during the reproduction of the digital dynamic image data to only adjustment of the phase of the sampling clock, thus lightening the load on the CPU or the like and improving the efficiency with which digital dynamic image data is reproduced.
Note that phase data in this case is data for adjusting any discrepancy in phase between the generated sampling clock and the desired sampling clock, and any suitable data can be used therefor, such as data expressing a time difference of several nanoseconds.
In addition it is preferable that the frequency and phase of the dot clock of each of these image generation devices is previously checked, and data is stored in a storage means for frequency data and phase data of each device, based on the results of the check.
(4) The synchronization signal may be a horizontal synchronization signal; and the clock generation means may adjust the phase of the sampling clock, based on at least one of the rise and fall of the horizontal synchronization signal together with the phase data.
This makes it possible to generate a suitable sampling clock by adjusting the phase of the sampling clock when there are variations in the horizontal synchronization signal. It is therefore possible to reproduce the digital dynamic image data more faithfully from the original digital dynamic image data, by sampling with a sampling clock with a thus-adjusted phase.
(5) The analog-digital conversion means may convert the analog dynamic image data into digital dynamic image data at the timing of at least one of the rise and fall of the sampling clock.
For example, there is a stable portion where there is no variation in the analog dynamic image data (signal) at the rise of the sampling clock, so it is possible to reproduce digital dynamic image data that is faithful to the source image by subjecting the analog dynamic image data (signal) to analog-digital conversion at that timing.
(6) The image reproduction device of this invention may further comprise transmission means for transmitting the reproduced digital dynamic image data via a transmission path to a digital animation processing device.
The computer-usable information embodied on an information storage medium may further comprise information for implementing (executing) the above described means. As an example of the information, there is a computer-usable program for implementing (executing) the above described means. This program could be embodied in a carrier wave.
In this way, the digital animation processing device that is the transmission goal can process digital dynamic image data that is faithful to the original digital dynamic image data.
In this case, transmission path is not limited to a wired communications line such as a cable; it could also include wireless means such as satellite communications. In addition, transmission is not just to an external device by cable; it could also be over a system bus within a device, for example.
If, for example, digital dynamic image data is transmitted over a cable from the image reproduction device to the other processing device, the image reproduction device can transmit digital dynamic image data that is faithful to the original digital dynamic image data.
This makes it possible for the other processing device to process data that is substantially the same as the original data.
(7) The digital animation processing device may be a digital animation display device.
A general-purpose image generation device is assumed to output to a TV or CRT monitor, so it outputs an analog dynamic image signal.
Since it is not assumed that this analog signal will be re-digitized, it does not comprise a dot clock signal.
However, in a digital animation display device that uses liquid crystal or the like for a liquid crystal means, the input analog dynamic image signal is re-digitized for display. During this digitization, signal disturbances can easily occur.
It is therefore necessary to provide adjustment (correction) means for manual operation on the digital animation display device side, to manually correct such disturbances in the signal.
This invention makes it possible to reproduce digital dynamic image data from analog dynamic image data, so that a digital animation display device can display a clear image that is faithful to the source image, without necessitating such correction.
(8) The digital dynamic image data may be dynamic image data for a game.
In this case, the image generation device that generates digital dynamic image data is limited to a game machine. This makes it easy to distinguish between different image generation devices. As a result, players can obtain good image quality, even when different game machines are connected for monitor output.
(9) This invention can also be applied to the processing of static image data, in addition to dynamic image data.